From paved road to the first creek crossing, about a mile in: The guides say this is doable in a 2wd car, but a 2wd truck would be better. I drug my Enclave over a rock on the way in and out. It is pretty flat, and 4wd is not needed. We stopped at the first creek crossing. From there, the hike was about 13 miles round trip.
From the creek crossing to just past Pearl Pass Bridge: If your vehicle can make it across the creek, the next really challenging section is about another mile away. The least capable vehicles I saw go through the creek were a Mercury Mariner (Ford Escape) and the latest model Honda Pilot. The creek was maybe 9" deep in the morning and afternoon.
The Hard Part: About 200 yards past Pearl Pass Bridge, the road turns hard left and goes sharply uphill. There are some big rocks and ruts in the way. A recent trip report has a picture of them. Once you get past this section, getting to end of the road is easier. I saw a stock Jeep, stock Forerunner (3rd newest generation), and stock old Chevy Blazer past this point. Low range for this section would be helpful. I was shocked to see that the newest model Honda Pilot made it past this point. I wouldn‘t recommend that. There is parking for about 3 cars just before this section. Cars that didn‘t attempt it included a Murano and an Xterra. I think the Xterra could have done it. At one point, the stream runs down the trail/road. Go straight up this section a few hundred yards and veer to the right. Once you get to the end of the road, there is plenty of parking.
Also, the last good bathroom is about two miles before the trailhead on the east side of the road. It‘s a vault toilet that is part of a park. It‘s easily visible if you look for it.